Belt-type expansion joints are commonly used in industry today to provide relief from stresses caused by thermal expansion and contraction in large duct systems, and to reduce the transmission of vibration and noise. The belt-type expansion joints commonly used today are rubber flexible members including one or more layers of a heat resistant fabric, such as asbestos fabric, and have been found to be more effective than metal expansion joints because of their greater flexibility in a shorter space and their ability to withstand the acidic gases that are commonly present in ducting systems. The rubber expansion joints are commonly made from an elastomer, such as neoprene, chlorobutyl rubber, or VITON (a copolymer of hexafluoropropylene and vinilidene fluoride having a specific gravity of 1.82) having one or more layers of asbestos cloth sandwiched therein. The belt-type expansion joints are sometimes manufactured having a chemical resistant layer, such as polytetrafluoroethylene, as a loose overlay to provide both for thermal resistance and chemical resistance.
In accordance with the present invention, it has been found that the vulcanization of a heat shield including a polyester film, such as polyethylene terephthalate, and an inner, gas-contacting metal foil, such as aluminum, to a belt-type expansion joint comprising an elastomer carrying a heat resistant fabric, such as an asbestos fabric, provides an exceptionally efficient and desirable flexible belt material having unusually and unexpectedly good properties of protection against heat, and chemical attack, and excellent properties of strength and long life when subjected to repeated temperature changes.